When it comes to under-the-radar health conditions, deep-vein thrombosis is at the top of the list. Most of my patients have never heard of this common problem. Yet deep-vein thrombosis puts more than one-quarter million Americans in the hospital each year, and complications from it are responsible for upwards of 100,000 deaths.

Deep-vein thrombosis (DVT) is the medical term for a blood clot that forms in a leg vein. Some DVTs cause no symptoms; others hurt, or make the leg swell. There are two big worries with a DVT:

Pulmonary embolism. A piece of a clot can break away, travel through the bloodstream, and become lodged in the lungs. This is called a pulmonary embolism. Almost all DVT-related deaths are due to a pulmonary embolism.

Post-phlebitis syndrome. A clot can permanently damage the vein it is lodged in. This problem, called post-phlebitis syndrome, causes persistent leg pain, swelling, darkened skin, and sometimes hard-to-heal skin ulcers. Up to 40% of people with a DVT develop post-phlebitis syndrome.

Treating DVT

Deep-vein thrombosis is initially treated with an anticoagulant such as heparin or fondaparinux. Anticoagulants can stop a DVT from getting larger and can prevent new clots from forming. Use of these drugs substantially decreases the risk of developing a pulmonary embolism.

But anticoagulants can’t dissolve a clot that has already formed. That’s the job of drugs called thrombolytics (commonly known as clot busters), such as streptokinase and alteplase. Although you might think that using these drugs against DVT would be a good idea, studies have had mixed results. Thrombolytics don’t appear to improve survival or shorten hospital stays, and they increase the risk of bleeding. They do, however, appear to decrease the risk of post-phlebitic syndrome.

A new study published online in The Lancet shows that delivering a clot-dissolving drug directly into the clot—instead of having it circulate through the bloodstream via standard intravenous delivery—is very effective in preventing post-phlebitic syndrome among people with large clots that are high up in the leg and/or in the pelvis. Direct delivery of the clot-buster allows the use of a lower dose, which decreases the risk of bleeding elsewhere in the body.

Not everyone with a DVT needs direct clot-dissolving therapy. Anticoagulants, along with support stockings to reduce swelling and improve blood flow, are enough for most people. For those with a large clot, especially one high up in the leg or in the pelvis, direct injection of a thrombolytic agent will help protect the affected vein from post-phlebitic syndrome.

Prevention is preferable to treatment

Anyone can develop a DVT, although some people are more likely to have one than others. You are at increased risk if you or a close family member have had a DVT before, have an inherited condition that causes your blood to clot more readily than normal, have cancer, are immobile for a long time (confined to bed, long-duration plane or car trip, etc.), or use birth control pills.

Here are some good ways that everyone can use to help prevent a DVT from forming:

Stay physically active. At work or at home, get up from your chair frequently. Short walks contract the muscles in your legs that help pump blood back toward your heart.

Avoid dehydration. This is especially important when you are going to be sitting for a prolonged time, such as in an airplane.

Move your legs. If you are bedridden and can’t take frequent walks, contracting your leg muscles will help prevent blood from pooling and clotting.

Maintain a healthy body weight. Obesity increases the risk of DVT.

If you are hospitalized for some reason, ask your doctors and nurses to make sure you are receiving measures—such as wearing special stockings or getting low-dose heparin—to prevent blood clots.